In recent years, high usage of mobile devices with Internet services has sparked an increase in wireless computing services providing real-time, contextual, and personalized applications. One of the key technologies contributing to this increase is positioning technology, which is capable of providing accurate location contexts relating to such mobile devices.
Location-based services (LBS) based on Global Positioning System (GPS) in mobile devices, especially in smart phones, have been gaining popularity over the last decade. However, accurate positioning via GPS is lost once a mobile device is moved indoors, or into dense urban areas. When indoors, GPS signals between the mobile device and satellite would lose line-of-sight and the GPS would cease to operate. In the case of urban areas, signal attenuation and multi-path effects caused by physical obstacles (mainly tall buildings) can make GPS signals undetectable.
Numerous techniques have been proposed to deal with situations where GPS service is not available. A cellular tower triangulation method serves as a solution for mobile devices with connectivity to cellular networks (e.g. GSM, UMTS, etc.). In this method, cellular towers whose geographical locations are known are used as reference points to calculate location of a mobile device communicating with them. While the method has an advantage of not requiring users to provide dedicated equipment in addition to those existing in a cellular network, cellular tower triangulation suffers from low positioning accuracy, which could, for instance, provide location readings that are above 50-100 meters off from the actual location.
Positioning technology based on Wireless Local Area Network (WLAN), in particular Wireless Fidelity (Wi-Fi) systems, has attracted research attention in both academic and industry communities. This is probably due to a fact that Wi-Fi systems are operating on a relatively high radio frequency and they have a much smaller coverage compared to cellular based systems. Both of these features contribute to higher positioning accuracy. Most Wi-Fi positioning solutions currently available are designed to track people or asset in a certain controlled premise, e.g. a hospital or a warehouse. However, most of such solutions require dedicated equipment, e.g. a Wi-Fi tag, to be attached to the person or asset in order for its location to be tracked. Furthermore, a data connection is usually required between the dedicated equipment and Wi-Fi access points for exchanging synchronization information before tracking takes place. Hence, currently available Wi-Fi positioning solutions are not workable without such dedicated equipment and conscious effort put in by a user to operate the system to track a person or asset.